This invention relates to a process for coating paper with paper-strengthening resins mainly composed of water-soluble thermosetting polyvinylamide polymers, which have the property of providing paper with a nearly constant wet and dry strength in the pH range of 3 to 10, the resins can be mixed, if desired, with other water-soluble polymers and various pigments.
Various processes for coating paper with resins which impart wet and dry strength to paper are known in the art. For example, there are processes for coating paper with urea and melamine resins, respectively. However, both of these processes are effective only in acid pH ranges, and moreover, manifest another disadvantage in that formalin gas is generated either in coating operations or from the resulting coated paper product. There is also a process for coating paper with polyamide-epichlorohydrin resins. This is efficient in alkaline pH ranges, but is of little effectiveness in acid, and furthermore, even in the alkaline pH ranges the resulting coated paper does not have enough dry strength. According to the above prior art, a coated paper with enough wet and dry strength is not obtained without curing at high temperatures.